1. Field of Invention
The present invention relates to a manufacturing method for a polarizing conversion element for converting incident non-polarized light into specified polarized light.
2. Description of Related Art
In a projector, a light-modulating device for modulating light corresponding to image signals is used. As the light-modulating device, the type of using only one type of linear polarized light, such as a transmissive liquid crystal panel and a reflective liquid crystal panel, is usually used. In the projector which only uses such one type of linear polarized light, a polarizing conversion element for converting emitted non-polarized light from a light source into one type of a linear polarized light component (S-polarized light component or P-polarized light component, for example) is provided.
FIGS. 8(A)-(B) are schematic representations showing a polarizing conversion element 320. FIG. 8(A) shows the polarizing conversion element 320 in the x-z plane, while FIG. 8(B) shows the polarizing conversion element 320 in the x-y plane.
The polarizing conversion element 320 may consist of a polarizing beam splitter array (polarized light separating element) 340 and a plurality of xcex/2 phase films 381 selectively arranged on portions of emitting surface of the polarizing beam splitter array 340. The polarizing beam splitter array 340 has a height of h and a shape in which a plurality of column-shaped light transmissive members 324, each having a parallelogram cross-section, are sequentially bonded to each other, and column-shaped light transmissive members 325 and 326, each having a trapezoidal cross-section, are respectively bonded to the two ends of the bonded members 324. Polarization separating films 331 and reflecting films 332 are alternately formed on each of boundary surfaces between light transmissive members 324, 325, and 326. The xcex/2 phase films 381 are selectively arranged at mapping portions in the x-direction of emitting light from the polarization separating film 331 or the reflecting film 332. In this example, the xcex/2 phase films 381 are selectively arranged at mapping portions in the x-direction of emitting light from the polarization separating film 331.
The polarizing conversion element 320 separates incident light on the polarization separating film 331 into an S-polarized light component and a P-polarized light component. The S-polarized light is reflected by the polarization separating film 331 and is further reflected by the reflecting film 332 to be emitted therefrom. On the other hand, the P-polarized light component is allowed to pass through the polarization separating film 331 just as it is. On the emitting surface of the transmitted light from the polarization separating film 331, the xcex/2 phase film 381 is arranged, whereby the P-polarized light component is transformed to the S-polarized light component to be emitted therefrom. Therefore, a set of the polarization separating film 331, the reflecting film 332, and the xcex/2 phase film 381, which adjoin each other, corresponds to one polarizing conversion unit. In addition, the polarizing conversion element 320 in this example has three lines of polarizing conversion unit 350 and one line of dummy unit 350d. In such a manner, the polarizing conversion element 320 is an optical element for converting incident light on the polarization separating film 331 into substantially one kind of a linearly polarized light component.
FIG. 9 is a schematic representation showing a manufacturing example for the polarizing beam splitter array 340. In the polarizing beam splitter array 340, for example, a first glass plate 321 having the polarization separating film 331 and the reflecting film 332 formed thereon and a second glass plate 322 having no film formed thereon are alternately bonded to each other by an optical adhesive 327, so that the polarization separating film 331 and the reflecting film 332 are alternately arranged. Then, an ultra violet ray (UV ray) is irradiated thereon to cure the optical adhesive 327. At this time, third glass plates 323 having a different thickness from that of the first and the second glass plates 321 and 322 are used as first and the last plates of the bonded plates, to form a composite plate member 400. Light transmissive blocks are cut substantially in parallel with each other off the composite plate member 400 formed as above along sections (shown by broken lines in the drawing) inclining at the predetermined angle xe2x80x9cxcex8xe2x80x9d with the surface of the composite plate member 400, using a multi-wire saw or a multi-blade saw. The value xe2x80x9cxcex8xe2x80x9d is preferably about 45xc2x0. Here, xe2x80x9cthe surface of the composite plate member 400xe2x80x9d indicates the surface of the third plates 323 bonded at the both ends. Protruding portions of both ends of the block are cut off by a dicing saw or a laser cutting apparatus so that the block has a substantially rectangular shape. Surfaces (cutting sections) of the light transmissive block cut in such a manner are polished to obtain the polarizing beam splitter array 340 (FIGS. 8(A)-(B)). In addition, portions formed by the first and the second glass plates 321 and 322 correspond to the light transmissive members 324, while one of the portions formed by the third glass plates 323 at one of the two ends corresponds to the light transmissive member 325, and the other thereof at the other end corresponds to the light transmissive member 326. The thickness of the third glass plate 323 corresponding to the light transmissive members 325 may be different from that of the third glass plate 323 corresponding to the light transmissive members 326.
In addition, the polarizing beam splitter array may be referred to as xe2x80x9ca light transmissive blockxe2x80x9d below.
Conventionally, the polarizing conversion element has been manufactured in the manner described above to improve efficiency. However, a further improvement in manufacturing efficiency is desirable.
The present invention is made to at least solve the above-mentioned problems, and it is an object of the present invention to at least provide a technology to manufacture a polarizing conversion element more efficiently.
Accordingly, a first method for manufacturing a polarizing conversion element according to the present invention may consist of the steps of:
preparing k sets of light transmissive members, k being an integer of 2 or greater, where each of the sets may consist of a plurality of first light transmissive plates and a plurality of second light transmissive plates having substantially a same thickness as that of the first light transmissive plates;
preparing (k+1) third light transmissive plates having a greater thickness than those of the first light transmissive plates and the second light transmissive plates;
producing a composite plate member by alternately arranging and bonding one set of the plurality of first light transmissive plates and the plurality of second light transmissive plates to each of spaces between the (k+1) third light transmissive plates, and alternately arranging a plurality of polarization separating films and a plurality of reflecting films on each interface between the first light transmissive plates, the second light transmissive plates and third light transmissive plates in the composite plate member;
producing a block substrate having a light receiving surface and a light emitting surface by cutting the composite plate member along a first section parallel to a surface inclining at a predetermined angle with a surface of the composite plate member, the light receiving surface and the light emitting surface being in parallel to the first section;
polishing the light receiving surface and the light emitting surface of the block substrate; and
producing k light transmissive blocks from the one block substrate by dividing the block substrate at positions of the third light transmissive plates disposed inside the block substrate.
A second method for manufacturing a polarizing conversion element according to the present invention may consist of the steps of:
preparing k sets of light transmissive members, k being an integer of 2 or greater, each of the sets comprising a plurality of first light transmissive plates and a plurality of second light transmissive plates;
preparing (k+1) third light transmissive plates having a greater thickness than those of the first light transmissive plates and the second light transmissive plates;
producing a composite plate member by alternately arranging and bonding one set of the plurality of first light transmissive plates and the plurality of second light transmissive plates to each of spaces between the (k+1) third light transmissive plates, and alternately arranging a plurality of polarization separating films and a plurality of reflecting films in each interface between the first light transmissive plates, the second light transmissive plates and the third light transmissive plates in the composite plate member;
producing a block substrate having a light receiving surface and a light emitting surface by cutting the composite plate member along a first section parallel to a surface inclining at a predetermined angle with a surface of the composite plate member, the light receiving surface and the light emitting surface being in parallel to the first section; and
producing k light transmissive blocks from one of the block substrates by dividing the block substrate at positions of the third light transmissive plates that are disposed inside the block substrate.
In the conventional manufacturing method, 2 k third light transmissive plates have to be prepared in order to produce k light transmissive blocks. However, in the manufacturing methods according to the present invention, (k+1) third light transmissive plates are enough to be prepared, whereby the number of parts for producing the polarizing conversion element can be reduced, resulting in reduction in the manufacturing cost.
In particular, according to the first manufacturing method of the present invention, a block substrate including k light transmissive blocks per one substrate is produced from a composite plate member; after the produced block substrate is polished, k light transmissive blocks per one substrate can be produced. Thereby, the number of steps for cutting the composite plate member and polishing the light receiving and light emitting surfaces can be reduced to be 1/k compared with that in producing k light transmissive blocks by a conventional manufacturing method, so that the polarizing conversion element can be more efficiently manufactured than ever.
In addition, preparing the k sets of light transmissive members may preferably consist of forming the polarization separating film on a first surface of the first light transmissive plate, and forming a reflecting film on a second surface of the first light transmissive plate. Also, preferably, preparing the k sets of light transmissive members may consist of forming a polarization separating film on one surface of the first light transmissive plate, and forming a reflecting film on one surface of the second light transmissive plate.
In either way, a plurality of polarization separating films and a plurality of reflecting films can be alternately arranged on each interface between light transmissive plates.
The above-mentioned manufacturing methods may further consist of dividing a light transmissive block of the light transmissive blocks produced from the one of the block substrates into a plurality of light transmissive blocks by cutting the light transmissive block along a second section in parallel with a surface substantially perpendicular to a longitudinal direction of the plurality of polarization separating films and the plurality of reflecting films arranged inside the light transmissive block.
In this manner, a plurality of light transmissive blocks can be produced from one light transmissive block produced, thereby enabling the polarizing conversion element to be manufactured more efficiently.
Further, the polarizing conversion element manufactured by above methods may be employed by a projector. In this manner, resulting in reduction in the manufacturing cost for manufacturing the projector and enabling the projector to be manufactured more efficiently.